Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy. Prior to treating the condition, one has to first determine the location of the wavelets. Various techniques have been proposed for making such a determination. One proposed technique provides for measurement of the activity within a pulmonary vein, coronary sinus or other generally-tubular structure in or around the heart, where the activity is simultaneously measured at multiple points about the inner circumference of the structure.
A catheter for performing such a technique is described in allowed U.S. patent application Ser. No. 09/551,467 now issued as U.S. Pat. No. 6,628,976 on Sep. 30, 2003, entitled “Catheter Having Mapping Assembly.” The catheter includes a generally-circular electrode assembly at the distal end of the catheter. The generally-circular electrode assembly is introduced into the pulmonary vein so that the outer circumference of the electrode assembly is in contact with an inner circumference of the pulmonary vein. Using electrodes arranged on the electrode assembly, the electrical activity all around that circumference can be measured. This method is much more effective and accurate than separately measuring individual points along the circumference, for example, with a standard straight catheter carrying only a single mapping electrode or mapping electrode pair.
However, the pulmonary vein can be somewhat irregular in shape. In such circumstances, a generally-circular electrode assembly as described above may not make sufficient contact with the inner circumference of the pulmonary vein. Accordingly, a need exists for a catheter than can take into account irregularities in the pulmonary vein and contact a sufficient portion of an inner circumference of the pulmonary vein to map multiple points along the circumference simultaneously.